1. Field of Technology
The present invention relates to the intermediate tone processing of a digital image data.
2. Description of the Prior Art
In an image processing apparatus such as an image reader or the like, an image of the original is read out by an image sensor such as, for example, a CCD (charge-coupled device) line sensor and, then, the image information so read out is digitized. The digitized image information is reproduced by means of an output device such as, for example, a laser printer.
In the case of an image of intermediate tone, an intermediate tone processing such as by means of a dither method is carried out at the time the image information is digitized. In general, when the intermediate tone processing is effected, the resolution tends to be lowered accompanied by the lowering of the contrast.
The human sense of sight is more sensitive to the contour of any image and, therefore, one will be unfavorably impressed if an image represents an indistinct contour.
In view of the foregoing, various attempts have hitherto been made to enhance the contour. By way of example, the Japanese Laid-open Patent Publication No. 59-43672, published in 1984, discloses an image processing device wherein the contour can be enhanced by means of one-dimensional convolution integration. On the other hand, according to the Japanese Laid-open Patent Publication No. 59-90461, published in 1984, a ROM conversion table is used to enhance the contour. The conventional method of the enhancement of the contour requires the use of a line memory or any other device such as ROM, rendering the apparatus as a whole to be complicated.